Process of molding polysulphide polymers



' Patented Nov. 12, 1940 UNITED STATES 2,221,650 moon ss or MOLDINGrousm'nmr. ronmns Joseph 0. Patrick, Morrisville, rs, assirnor toThiokol Corporation, tion of Delaware No Drawing.

columns.

This invention relates to a new synthetic plastic having a very highdegree of utility in the arts due to its combination of specialproperties. The generic chemical constitution dfthe basic material ofthe present invention has a certain generaloutline common to allspecies.

Houses have certain general outlines in common, yet the comfort andutility of a house depends to alarge extent on the manner in which theindividual rooms and-other parts of the house are constructed andarranged.

So in my'invention, within the general outline or structure common tothe molecule of my synthetic compound, I have found that I can varythenature and arrangement of the atoms, to adapt the properties of thecompound to a variety of special uses.

This controlled adaptability is one of the features ofthi's inventionand as a result thereof products having a variety of difi'erent uses canbe produced as indicated by the following list:

Oil and solvent proof gaskets, washers, etc., tubing and hose, resilientrolls such as printers rollers, elasticsheets, etc. The material hasalso been pressed into cloth, asbestos and other textile fiber to formlaminated articles, pump diaphragms and suchmaterials.

The plastic materials described herein have been made into printingplates and other complex shapes'such as molded electrical insulativeparts to which use its particular physical character peculiarly fits it.

This invention is a continuation-in-part of my 'copending applicationSerial No. 38,209, filed 85 August 28, 1935, and Serial No. 107,167,filed October 23, 1936.

' Another feature is the rapidity with which articles can be produced,e. g. by molding the product of my invention. This is a matter of greatof the molding operation. In this operation, a

workman places a charge of plastic material in a metallic mold in whichthe plastic is heated and pressed until it can be safely removed fromthe mold. The cost of the finished article, apart from the cost of theplastic material, depends upon the number of molded articles which canbe produced per man, per hour, per mold. Thus if an article requires 50mintues in the commercial importance because of the economics mold, theproduction cost of the article is much greater than that of one whichrequires only 5' Yardville, N. 1., a corpora- 1 Application December 9,1931, Serial No. 179,015

ities with production speed, is, I believe, an im-' portant forward stepin the plastic industry.

Another feature is the fact that results can be attained therebyotherwise not capable of realization.

Until the present invention, the production of articles having a highdegree of resiliency, resembling vulcanized rubber in this respect, by aforming operation requiring only a few moments application of heat andpressure, has never been attained. Attempts to do this with naturalrubber have been unsuccessful. For example, particles of cured rubberwill not satisfactorily coalesce without the use of a binder and in thatcase the rubber acts largely as a filler, the real molding materialbeing the binder.

In accordance with. the present invention, an autogeneous welding of thearticles may be effected at moderate temperatures and pressure, yieldingthe totally unpredictable result that a formed article is producedhaving a perfectly continuous single phase structure and possessing thesame, or better, physical properties such as tensile strength,elongation, resistancetotear, etc., than the cured material possessedbefore being reduced to the powdered state.

As to the general outline of structure of the synthetic material, it isat least in its intermedi- R stands for an organic radical. Sx signifiesa group of sulphur atoms, e. g., two to six. Thus the general outline ofthe structure of the said material can be described as an organicradical alternating with a group of sulphur atoms and constituting along chain molecule. By varying the number of sulphur atoms in the groupthereof and/or by varying the nature of the organic radical R, materialhaving special and unique properties can be obtained.

To illustrate how said properties may be obtained coupled with highspeed production ofmolded articles, made therefrom, an example will begiven, the word polymer used therein meaning the organic polymer inintermediate form having the general structure above described andproduced as hereinafter fully set forth.

Example 1 Parts by weight Polymer 100.00 Zinc nxirle' 10.00 Carbon black60.00 Stearic aci .50 .Benzo thiazyl disulphide (Altax) .25

The aboveoingredients are mixed by mastication and the resulting mixtureformed into sheets.

The zinc oxide acts as an oxidizing agent. Instead of ZnO, otheroxidizing agents can be used including oxides and peroxides of lead,bismuth, arsenic, manganese, various oxidizing salts, e. g. bichromates,perborates, etc., and organic oxidizing agents including organicperoxides and nitro and polynitro compounds.

Example 2.Tfiis material is heated, e. g. to around 300 F. for about anhour. It undergoes a transformation which develops its desirableproperties. This transformation can be called curing. In theintermediate form above mentioned, these properties are inchoate. In thecured form these properties become developed or consummate. They includetoughness, elasticity and resistance to permanent deformation.

Formerly, the product sold by the manufacturer was the intermediatepolymer above, mentioned. He sold it to the consumer who mixed it as inthe above Example 1 and cured it as in Example 2. This is stilltheprocedure for "many purposes. But for molded articles, the long time ofthe curing process was a disadvantage because of the cost.

Molds, especially those of the more intricate designs for which thismaterial is uniquely suited, are expensive and the process whichsubstitutes a simple molding operation of say, five minutes, for themore complex curing and forming operation requiring from 50 to 60minutes, gives a tenfold output per mold or conversely reduces the costof the molds required for a given capacity to one-tenth. The sameeconomies apply to the presses and labor required.

I have found that the cured material produced as for instance in Example2 can'be reformed. For example, the fully cured material may becomminuted or powdered and the material so produced reformed veryquickly. Not only are the valuable properties not impaired but in mostcases are enhanced. What formerly was the molders finished product nowbecomes his raw material so far as the substance is concerned. He nolonger carries out the time consuming curing operation in molds. Thecuring operation'is carried out by the manufacturer of the polymer. Thispolymer is cured in bulk rather than molds and the molder buys a curedmaterial. In the curing operation, by using large open steam curers orvulcanizers, one man can cure tons of the material, i. e., the outputper man per hour is very high, far greater than the output per man perhour if the curing occurred in molds.

This cured material above mentioned possesses the unsuspected and uniquecapability of being remolded.

In accordance with my invention, three stages or steps are undertaken,to wit:

1. Production of polymer.

2. Curing of polymer.

3. Remolding of the cured polymer to yield formed elastic article.

Example 2 above illustrates the curing step. The remolding of the curedpolymer is illustrated by the following example.

Example 3.-The product produced as in Example 2 is ground to a powder orcomminuted into particles of a convenient size. The powder is thenplaced in a mold and heated and pressed therein for a period, of say 2to 10 minutes (depending on the size of the article). It may then beremoved from the mold without cool ng, 1 dropped hot.

This invention utilizes the discovery that, after the curing step,the'cured material still retains the capacity to undergo a reformingoperation; that after the curing step the cured material can be takenapart or disintegrated and put together again; that the putting togetherinvolves no loss' of valuable properties, but, on the contrary, anenhancement of such properties; that such putting together can beaccomplished in a fraction of the time required for the curing operation10 with resulting marked economic and technical ains.

Furthermore, the divided and pulverulent form of this molding materialpermits the escape of air and gases from the article during the moldingprocess and allows the forming of highly complex articles with perfectfidelity to the mold contour which would not be possible if a solidpiece of material were placed in the mold.

The initial polymer may be obtained by various means illustrated by thefollowing:

(a) Reaction of an alkaline polysulphide with an organic compound havinga substituent on each of two different carbon atoms which substituent issplit off during the reaction. This reaction produces a polymer havingan organic radical alternating with a group of three, four, five or sixsulphur atoms, depending on the particular alkaline polysulphideemployed.

(1)) Process according to (a) followed by a partial desulphurization.This-results in a polymer having a pair of sulphur atoms alternatingwith an organic radical.

(c) Oxidation of poly functional mercaptans,

i. e., organic bodies having -SH groups attached to each of two or moredifferent carbon atoms. This leads to a product having a pair of sulphuratoms alternating with an organic radical.

There are other methods of producing the polymer, but these will besufficient to serve as 60 illustrations.

Processes (12) and (0) each lead to a polymer having a pair of sulphuratoms alternating with an organic radical, whereas process (a) isemployed to produce a polymer having a group of 5 three or more sulphuratoms alternating with an organic radical. The polymers produced byprocess (a) are herein called polysulphide polymers and those producedby processes (b) and (c) are herein called disulphide polymers. Therespective merits of the disulphide polymers and the polysulphidepolymers for the purposes of this invention will be pointed out.

The influence of the nature of the organic radical alternating with thesaid group of sulphur atoms will also be set forth. This exposition willbe assisted by several examples, as follows:

Example 4.-Preparation of a polysulphide polymer. 3000 liters of 2 molarsodium tetrasulphide solution containing 6000 gram mols of 00 thetetrasulphide are treated with 8 kilograms of NaOH followed by 20kilograms of MgClzfiHzO- in a reaction vessel provided with coils forheating and cooling and an agitator. Then 3000 mols or about 297kilograms of ethylene dichlo- 06 ride are gradually added during about 3hours at a temperature of about 160 F. After all the ethylene dichloridehas been added the temperature is raised to about 200 F. and maintainedthere for about 3 hours.

The reaction product is then settled and a polymer separates on standinin the form 'of a latex-like liquid. The mother liquor is siphoned offandthe said latex is washed several times with water. This can be donereadily because the 75 latex has the peculiar property of mixing intimately with water and then separating out therefrom by gravity. Washing.is continued until substantially all water-soluble impurities areremoved. The washing is thorough because of the ultramicroscopic size ofthe particles of polymer .in the latex.

in Example 1, cured as in Example 2, and reformed as in Example 3, andafter reforming has properties as follows:

Tensile strength lbs./sq. 111.. 10nd Elongation per cent 500 Permanentset after elongation .do 20 The reaction of the sodium polysulphide withthe ethylene dichloride is one in which the chlorine is split OE and itsplace taken by a polysulphur group. See Equations A to D below. There isno question that this splitting ofl occurs, be-' cause sodium chlorideis one of the by-products. Instead of chlorine, other substituents whichare split off may be employed, including bromine, iodine, nitrate,sulfate, carbonate, acetate, propionate, etc., and numerous othersubstituents which are split ofl in the reaction.

Instead of the ethylene dichloride used in the above example, any memberof the list set forth below could be used, X and X signifying asubstituent on each of two different carbon atoms which substituent issplit ofi during the reaction. This list is classified into variousclasses and the influence of the structure characterizing each classwill be described.

Class A.Where there is a saturated hydrocarbon having a replaceablesubstituent substituted for a hydrogen atom on each of two difler- ,entcarbon atoms, or which the carbon atoms (to which the replaceablesubstituents are joined) are attached to and separated by straight chaincarbon atoms. l

, x(cH, nx'

n may be 1 to 20 or more CH:.CH.CH.CH:

"x x p 2, 3, disubstltuted butane clitafllfllllfls 2; 3, disubstitutedpropane CHa.CHI.(I7H.CHs.(IIH-CHLCHI x x 3, 5, disubstituted heptaneClass B.Where the carbon atoms (to which the replaceable substituentsare joined) are attached to and separated by branched chain saturatedcarbon atoms.

X.CH:.(|3H.CH:.X'

Disubstituted isobutane X.CH2.CH.CHI.X'

Disubstituted isopentane Class C. .Where the replaceable carbon atoms(to which the substituents are joined) are attached to and separated byatomic, structure characterized byan ether or thio ether linkage.

x.CgH .0-C2 4-x' Disubstituted ethyl ether X.CH.0.CH$X' I Disubstitutedmethyl ether x.c,H.o.c.n..oc,H..x' Disubstituted ethoxy ethyl etherx.c,H..s.c,H..x' Disubstituted thip ethyl ether x.c'n,.s.cH,.x'Disubstituted thio methyl ether CHI xcmobmdomoomm Dlsubstituted 1,3methoxy, 2, 2 dimethyl propane xmncrnoH,.o.oH,;o.cH,.oH,.oH,x'

Disubstituteddipropyl formal Disubstituted diethyltormal Disubstituteddimethoxy ethane Disubstltuted para diethoxy benzeneX.CH,0.CH,.CH,.0CH,.X' Disubstituted dimethoxy ethaneX.CH,.CH,.CH,.S.CH,CH,.CH .X' Disubstituted dipropyl thio etherDisubstituted diethyl carbonate Class D.Where the carbon atoms (to whichi the replaceable substituents are joined) are .at-

tached to and separated by atomic structure characterized by unsaturatedcarbon atoms.

' X.CHzCH=CH.CHzX

Disubstituted butene 2, 3

Dlsubstituted 3 tolyl propane 2,3 Class E.Where the carbon atoms (towhich the replaceable'substituents are joined) are attached toandvseparated by atomic structure characterized by an aryl group.

xcmOomx' Disubstituted para xylene Disubstituted para ethyl butylbenzene As to Class A compounds, as the number of carbon atoms in theorganic radical increases, elasticity of the cured polymer producedtherefrom decreases; resistance to hydrocarbon solvents decreasessomewhat.

By choosing a compound from Class B, elasticityof the cured polymer.produced therefrom is greater for a given number of carbon atoms, ascompared with Class A compounds.

By choosing a compound from Group C, elasticity of the cured polymerproduced therefrom is greater (for a given length of chain) than is thecase in Groups A and B. Moreover the remarkable property of retainingthe elasticity at low temperatures is also obtained thereby.

In general, Class D compounds produce properties similar to'Class C. Thecommon property in Class C and D compounds that is responsible forcertain common characteristics of polymers made from members of thesegroups is unsaturation.

The oxygen and sulphur of the ether and thio ether linkages in Class Ccompounds is unsaturated and so are the carbon atoms in Class D.

As to Class E, "the tendency of the aromatic structure is to decreaseelasticity and increase hardness, i. e., to produce compounds having aresinous, as distinguished from a rubbery, property.

The preparation of a typical disulphide polymer will now be described,together with an exposition of the influence of the organic radical insaid disulphide polymers and a comparison of disulfide polymers withpolysulphide polymers.

Example 5.--Preparation of a disulphide polymer by partialdesulphurization of a polysulphide polymer:

3000 liters of 2 molar sodium tetrasulphide solution containing 1044kilograms or 6000 gram mols of sodium tetra sulphide are treated with 8kilograms of NaOH followed by 20 kilograms of MgC12.6I-I2O in a reactionvessel provided with coils for heating and cooling and an agitator. 5400gram mols of 3-H dichlorethyl ether or 772 kilograms are slowly added tothe polysulphide mix during a period, of about three hours. The initialtemperature should be about 130 F. and should not be permitted to riseabove about 200 F. during the addition of the dichloro ether. After thedichloro ether is all in the reaction the temperature is raised to about210 F. and held there for about an hour with continued agitation tocomplete the reaction. The reaction mix is then cooled to about 150 F.The reaction product is a polysulphide polymer in the form of alatex-like liquid of such character that it can be washed and settledout from the washingwater. Upon standing, the latex settles from themother liquor which is drawn off and an equal volume of water is addedto restore the volume to that previously existing. The latex is thentreated with 250 kilograms of sodium hydroxide to effect partialdesulphurization. The temperature is again raised through a period ofabout 1 hour to about 210 F. and is maintained at that temperature forabout 15 minutes. The latex is then allowed to settle out of thereactionliquid. The reaction liquid is then withdrawn from above the settledlatex and is washed once by diluting largely with water and allowing thelatex to settle again with subsequent withdrawal of the supernatentliquid. The latex is diluted with water and 100 kilograms of sodiummonosulp'hide NazS is added to the latex water mixture, the volume ofwhich should be about 60 00 liters. The mixture is heated withcontinuous agitation to 210 F. and that temperature is maintained for aperiod of about 1 hour to effect completion of the partialdesulphurization, leaving the polymer substantially a disulphidereaction product.

All water soluble material is now removed from the latex by rapiddilution with clean water with subsequent settling out of the latex andremoval of the supernatant liquid. After complete remo al of watersoluble material by the washing process, a further purification may beeifected by blowing steam through the latex to, remove volatileimpurities.

Subsequent thereto, coagulation of latex and production of the polymerin massive formt occurs as in Example 4.

The polymer so produced maybe compounded as in Example 1, cured as inExample 2, and remolded as in Example 3.

The physical properties of the remolded compound are as follows:

Tensile strength-"A lbs./sq. in About 1800 Elongation per cent About 400Permanent set do About 15 Hardness About '72 Lowest temperature at whichelasticity is maintained", About 40 F.

Instead of the 3-3 dichlorethyl ether used in the above Example 5, anyother member of the list of compounds above set forth could be employed,and in this way I can therefore produce disulphide polymerscharacterized by apair of sulphur atoms alternating with an organicradical R selected from any of the classes set forth in the above list,that is, where R is a saturated straight chain hydrocarbon, a saturatedbranched chain hydrocarbon, a structure characterized by an ether orthio ether linkage, a structure characterized by unsaturated carbonatoms, a structure characterized by an aryl group, and finally amiscellaneous group, and. I will now point out certain relativedifferences between various classes of disulphide'polymers (and theultimate products produced therefrom) on the one hand and thecorresponding tetrasulphide polymers on the other hand. Disulphideproducts from disubstitutedstraight chain hydrocarbons (Class Acompounds) are hard resinous compounds, whereas the correspondingtetrasulphide products are of a rubbery character. Disulphide productsderived from ClassB compounds are of a definitely elastic and extensiblecharacter and possess these properties to a higher degree than thecorresponding tetrasulphide products. The disulphide products producedfrom Class C compounds are much more elastic and rubbery than thetetrasulphide products produced from the same compounds. The relationbetween the properties of the disulphide products in Class D compoundsand the corresponding tetrasulphide products is similar to the relationbetween the disulphide and tetrasulphide products from Class Ccompounds. The disulphide products from Class E compounds are in generalof a resinous nature. The disulphide products from Class E compoundshave a tendency to be hard and resinous in character and theseproperties are much more accentuated than in the correspondingtetrasulphide products.

As above mentioned, the disulphide products from Class A compounds havea tendency toward Class A and'another one from Class C or D andsimultaneously reacting this mixture of com pounds with sodiumpolysulphide, followed by partial desulphurization.

A specific example of such a procedure is set forth below:

Example 6,-5000 liters of 2 molar tetrasulphide solution-containing 1044kilograms or 6000 gram mols of sodium tetrasulphide are treated with 8kilograms of caustic soda followed'by 20 kilo- Q grams of MgClaGI-IzO ina reaction vessel provided ethylene dichloride and 1000 gram mols of 3-3a liquid of such character that it can be washed and with coils forheating and cooling, and an agitator. A mixture is made of 5000 grammols of dichlorethyl ether and this mixture is slowly added to thepolysulphide mix during a period of about 3 hours. The temperature ismaintained at about 160 F. during this time with continuous agitation.After all the mixture of organic reactant is in the reaction, thetemperature is raised to about 210 F. and held at that tempera-- turefor about an hour. The reaction product is a polysulphide polymer in theform of a latex-like settled out from the washing water. Furtherprocedure occurs as in Example 5, except that upon acidificationcoagulation into the form of a plastic mass does not occur, but ratherthe precipitation of a thin granular powder which settles to the bottomof the vessel in which acidification occurs and is then filtered oil. Itcan be dried,

by any suitable means, as for example in avacuum sheli' dryer.

Thereafter it is compounded as in Example 1, cured as in Example 2, andthen remolded as in Example 3.

This product has a unique combination of hardness and elasticity.- Itshardness is over 100 as measured on the Shore durometer and thishardness is combined in such a high degree with elasticity that theproduct can be struck a heavy blow without shattering.

Example 7.Preparation of a disulphide polymer, by oxidation of anorganic body having an SH group attached to each of two different carbonatoms.

138 lbs. or 1 mol of dimercapto ethyl ether,

are dissolved in 100 gallons sodium hydroxide solution containing 90lbs. of NaOH; that is, an amount of NaOH slightly in excess of '2 mols.With this solution there is intimately mixed a freshly preparedsuspension of magnesium hydroxide made by treating 10 pounds ofMgCl2.6HaO

with 2 gallons of water and adding thereto a solution of 4 lbs. NaOHdissolved in 0.5 gallon of water. The entire mixture is then placed in areaction vessel provided with stirring means and also means for heating,for example, steam coils. The mixture is subjected to stirring and tothis is gradually added an oxidizing agent in the form of a solution ofsodium polysulphide made, for example, by dissolving 348 lbs. or 2 molsof sodium tetrasulphide in one liter of water during a period of aboutten minutes. The reaction occurs approximately at room temperature andis "somewhat exothermic. The reaction is substantially completed afterall the polysulphide has been added.

The completion of the reaction is indicated by withdrawing a sample,acidifying it and observing whether the odor of mercaptan is absent.Stirring may be continued until the reaction is completed as indicatedby this test.

The polysulphide'acts as an oxidizing agent and converts the dimercaptoethyl ether into a complex polymer orplastic. The advantage of themagnesium hydroxide is that the said polymer or plastic is produced inthe form of a latexlike liquidwhich has the unique property of beingcapable of intimate mixture with water and settling out subsequently bythe action oi gravity. This property permits intimate and thoroughwashing to remove soluble impurities. Acidification of thelatex-like'liqdid causes the separation of polymer as an agglomeratedmass, the removal or the impurities from which would be a dimcultproblem. Itis'therefore highly desirable to accomplish the washing whilethis mass is in dispersed form, inasmuch-as under such conditions thehigh degree of dispersion of the. polymer permits an extremely thoroughremoval of the soluble impurities by washing. The difli-' culty ortransporting the latex in agglomerated form, and the ease with which itsticks to parts of apparatus, such as the stirrer, alsomakes itadvisabie to produce the polymer in the reaction vessel in its dispersedlatex-like form, from which vesselit can be readily removed because ofits,

fiuid characteristics. If the polymer were produced in the reactionvessel in its coagulated rubbery form, it would be difiicult to removeit therefrom and it would be contaminated with the re agents used in'itsmanufacture.

Washing of the polymer in its dispersed conditlon may be accomplished inthe reaction vessel by stirring it vup with successive quantities ofwater, settling and-drawing off the supernatant wash liquid. The washingcan, of course, be accomplished in a different vessel. In any event,

' it is desirable to preserve'the polymer in its dispersed conditionuntil after removal from the re- I action vessel. 1

The washed latex is then transferred to a sec- 0nd vessel wherecoagulation or agglomeration is produced by acidification. Suiiicientacid may be added for this purpose until'the mother liquid is acid tomethyl orange or brought to a pH of about 3. The coagulated polymer isthen dehydrated by any suitable method, e. g., milling, mastication orkneading. Insuch processes, considerable heat is generated which,together with the mechanical action, causes the removal of water.

In the above example, instead of sodium hydroxide as the agent fordissolvingthe dimercapto compound, other alkaline hydroxides could beused, for example, potassium, ammonisulphides may be employed, e. g.potassium and ammonium polysulphide or any, other soluble polysulphide.Other oxidizing agents may be used, for example, oxygen, air, ozone,hypohalites, and in general any oxidizing agent ef- "fective in analkaline solution, for example, hy-

drogen peroxide and metallic peroxides, perborates, chromates,dichromates, manganates and permanganates, etc. The reaction ispreferably carried on under alkaline conditions because it has beenfound that the reaction is very favorably influenced by such conditions.

Although in the above example, the step of agglomerating or coagulatingthe polymer was specifically described, it is in some cases-advantageousto preserve the polymer in its dispersed form as such, e. g., for use incoating and impregnating various materials.

The product obtained in this case is a white coagulum which, upondrying, is in thin sheets, a pale amber translucent and highly elasticsolid.

It is compounded as in Example I, cured as in Example 2, and remolded asin Example 3.

In the above example, instead of dimercapto ethyl ether, any othermember of the list above set forth can be used, where X and X signifyrespectively an SH group attached to each of two different carbon atoms.

In general, polymers and products produced by oxidizing mercaptocompounds, as described, have properties substantially the same as thoseobtained by the polysulphide reaction followed by partialdesulphurization.

As above mentioned, and specifically described in Example 6, a producthaving a unique combination of hardness. and elasticity may be produoedby preparing a blend of a disulphide polymerproduced from a Class Acompound with a disulphide polymer produced from a Class C or Dcompound. According to Example 6 this blend was conveniently made byreacting a mixture of a Class A compound and a Class C or D compoundwith an alkaline polysulphide and effecting a partial desulphurizationof the product. Similar results can be obtained by mixing a Class Acompound and a Class C or D compound, where however X and X are both SHgroups and then oxidizing this mixture to produce the blended disulphidepolymer according to the technique set forth in Example 7.

Formation of polysulphide polymers occurs as follows:

In this series of reactions X and X represent replaceable substituentsattached to each of two different carbon atoms, respectively, thesecarbon atoms being a part of an organic radical represented by R. Suchreplaceable substituents are split ofi during the reaction and may behalogen, sulphate, nitrate, phosphate, carbonate, acetate, propionate,etc.

This continues until a long chain is built up having the formula aaamsoThis loses the substituent X and acquires SH terminals as follows:

polymers may be built up from relatively low molecular weight startingmaterials, by reaction 20 with an alkaline polysulphide, e. g., sodium,potassium, ammonium, calcium, barium and other polysulphides.

The reaction is of great commercial importance because of the valuableand unique properties of the polymers, i. e., the products synthesizedby the reaction mentioned.

The starting material has two replaceable, i, e., substituents, each ona difierent carbon atom. Replacement of one of these substituentsproduces a molecule, which has the power to join hands with a similarmolecule, as shown above in Equations A to F. This joining goes on untila long chain is built up, the general structure of which issubstantiated by numerous reactions and tests including X-ray diagrams.

Partial desulphurization of polysulphide polymers to disulphide polymersoccurs as follows;

S ll

...R.S.SI.R...2S=.. R.S.S.R 40

Formation of disulphide polymers by oxidation of dimercapto bodiesoccurs as follows:

The mechanism of polymer formation consists in the removal ofH-atomsfrom mercaptan terminals by oxidation thus:

where oxygen or an oxygen-yielding oxidizing agent is used. The dimerthus formed again reacts with oxygen to form a tetramer. This thenreacts to form an octomer and finally a long chain polymer results withmercaptan or mercaptide terminals. Thus, when the reaction is carriedout in a sodium hydroxide solution the polymer has the formulaNaS.R.S.S.R.S.S......S.S.R.SNa

In this condition the polymer remains in a highly dispersed form inalkaline solution in the presence of a dispersing agent and can bewashed free of impurities, prior to coagulation. Owing to this property,the thoroughly washed dispersion or latex yields a coagulum free fromwater soluble impurities and electrolytes, which if allowed to remainwould impair its useful properties.

Upon acidification, the dispersion is coagulated and the polymerseparates as a rubber-like plastic mass. In that condition the metallicterminals are convert-ed into hydrogen and the polymer has the formulaHSR.S.S.R.S.S. R.S.S.R.SH

X-ray patterns show that the maximum distance between the organicradicals is not more thantwo sulphur atoms, even in the case of thepolysulphidepolymers.

The polysulphidepolymers therefore have the structure other sulphuratoms are loosely bound and can readily be removed by heating with apartial desulphurizing agent, e. g. NaOH or NazS or both.-

As already mentioned, one of the particular 35 uses of the presentinvention is the manufacture of complex shapes, such as printing plates.When printing plates are made of metal, many difficulties areencountered and unsatisfactory results are often obtained. The printingsurfaces 40 of such plates are rigid and unyielding and therefore greatcare must be exercised in placing them in .the machines, and it is oftennecessary to .take

the plates out of the machines and place thin shims under them to raiseor adjust them to the proper height for printing. This sometimesrequires repeated eflort and final adjustment and must be leftlto thejudgment of the pressman. If 5 printing surfaces extend too faroutwardly there is danger of cutting the surface that is to be printedor of breaking such a surface when it is brittle. The metal surfaces arealso sometimes attacked by the inks and by the solvents that are usedforremoving hardened ink from the plates. The plates must be protectedfrom rust or corrosion while they are not in use, thereby requiringcareful attention for keeping them uninlured. By the present invention,printing plates are made rapidly and economically and these plates arenot attacked by inks or solvents for inks and no special care need beexercised in keeping them for reuse.

I claim: 1. The process which comprises subjecting to heat and pressureamass of comminuted particles of a cured polymeric product substantiallyidentical with that obtained by reacting an alkaline polysulphide and anorganic compound having two carbon atoms to each of which is attached asubstituent which is split ofi during said reaction whereby a polymer isobtained and ouring said polymer.

2. The process of subjecting to heat and pressure a. mass of comminutedparticles of a. polymeric product comprising a precured polymersubstantially identical with that obtained by reacting an alkalinepolysulphide with an organic compound having two carbon atoms to each ofwhich is attached a substituentwhich is split olf during the reaction,thereafter reacting said polymer with a desulphurizing agent andpartially desulphurizing it and thereafter curing said par-tiallydesulphurized polymer.

' JOSEPH C. PATRICK.

